Magnetic actuators



I NVENTOR Mi segades 8c lDmufl'zas ATTORNEYS E.l R. BURDETT MAGNETIC ACTUATORS Filed Aug. 4. 1967 y Oct.vv 7, 1969- Edward Raymond Burdet? BY U.S. Cl. 335-174 10 Claims ABSTRACT OF THE DISCLOSURE A magnetic actuator for an electric vacuum switch has a casing carrying a roller which engages a cam. A push rod, which passes through the casing, is connected between the movable contact of the switch and an armature plate. Rotation of the cam brings the casing into contact with the armature plate whereupon energisation of a holding coil carried by the casing holds the armature plate in contact with the casing magnetically so that the armature plate moves with the casing during further rotation of the cam to close the contacts of the switch and compress springs which load the movable contact to its open position. Subsequent de-energisation of the holding coil, or energisation of a trip coil carried by the casing, permits the springs to overcome the magnetic force holding the armature plate in contact with the casing and move the movable contact to its open position.

This invention relates to magnetic actuators and has particular, though not exclusive, application to the provision of actuating means for the movable contacts of electric switches.

According to this invention a magnetic actuator includes actuating means, a movable element, means for imparting a cycle of reciprocatory motion to said movable element, the initial stroke of said cycle bringing said movable element into contact with a surface defined on said actuating means, magnetic flux producing means for producing a magnetic force which holds said surface in contact with said movable element when such contact is made so that said actuating means is moved with said movable element during the return stroke of said cycle, and means for subsequently reducing the magnitude of said magnetic force sufliciently for permitting said surface to move away from said movable element. Preferably said magnetic actuator includes means to produce a force acting on said actuating means in the direction of the initial stroke of said cycle, said surface being moved away from said movable element by said force when the magnitude of said magnetic force is reduced.

In a preferred application of this invention the magnetic actuator may be associated with an electric switch, the actuating means of said magnetic actuator being connected to a movable contact of said electric switch to move said movable contact into or out of engagement with the cooperating contact of said electric switch.

Electric vacuum switches capable of interrupting large fault currents require a higher contact pressure and a higlher speed of contact separation than hitherto; moreover the need for higher withstand voltages results in a requirement for a greater contact separation when in the open position. Whilst closing the contacts of such a vacuum switch it is desirab-le to move the movable contact rapidly towards its co-operating contact during the initial stages of a closing movement and then to progressively slow it down as it approaches the point of engagement with the co-operating contact in order to reduce the impact forces and thus reduce the likelihood of damage 3,471,814 Patented Oct. 7 1969 occurring to the contact surfaces upon engagement of the contacts. The application of a magnetic actuator in accordance with this invention as an actuating mechanism for a movable contact of an electric vacuum switch may enable the foregoing requirements to be met and, in the typical example described hereinafter, enables the contacts of an electric vacuum switch to be held together with a force of 500 lbs., to be opened in less than l0 milliseconds and permits a contact separation of between 0.5 and 1.0 inch.

One embodiment of the invention will now be described with reference to the accompanying drawing which shows diagrammatically an electric vacuum switch having associated therewith a magnetic actuator constructed in accordance with the invention.

Referring to the drawing the electric vacuum switch comprises a fixed contact 8 which co-operates with a movable contact 9. Th contacts 8, 9 are housed in a chamber 10 wlhidh is evacuated. The contacts 8, 9 and the chamber 10 may be of any desired construction in accordance with vacuum switch practice, and are therefore not described in detail.

A magnetic actuator 7 is provided for opening and closing the contacts 8, 9. The magnetic actuator 7 includes a movable element comprising a casing 11 of ferro-magnetic material having an annular part 11A in which is housed an electro-magnetic holding coil 12 and a trip coil 13. The actuating means of the magnetic actuator 7 comprises an armature 14 and a push rod 15 which is connected to the movable contact 9. The armature 14 is in the form of a flat plate of ferro-magnetic material. The end of the push 4rod 1S remote from the movable contact 9 is secured to a face 14A of the armature plate 14 so that the push rod 15 protrudes therefrom and extends through the bore 16 of the annular part 11A. The face 14A provides a surface of the actuating means which is adjacent and'substantially parallel to the lower face 11B of the annular part 11A. The push rod 15 is mounted within bearings 17 mounted at each end of the bore 16 so as to be capable of movement axially of the bore 16 relative to the casing 11. The casing 11 is mounted in spaced upper and lower bearings 18 in an external frame 19, the bearings 18 being conveniently mounted in spaced upper and lower transverse flanges 19A of the frame 19 to allow movement of the casing 11 in a direction parallel to the axis of the bore 16. That part of the casing 11 wlhich is slidably supported by the lower bearing 18 comprises a central rod-like extension 20 which carries a roller 21 below the lower bearing 18. The roller 21 cooperates with a shaped cam 22 which may be rotated by a motor 23 mounted on the frame 19 to impart a cycle of reciprocatory motion to the casing 11.

The roller 21, which acts as -a cam follower, Amay remain in contact with Ithe cam 22 under the influence of gravity, `or may be assisted, for example by light springs 24 between the casing 11 and the upper transverse flange 19A.

The push rod 15 carries a flange 25 above the upper end of the casing 11 (that is on the side of the annular part 11A remote from the armature plate 14). The flange 25 is loaded downwards by release Isprings 26, which 'are shown as coil springs in compression between the frame 19 and the llange 25. Stops 27, which are mounted on the upper face of the upper transverse flange 19A, co-operate with the underside of the flange 25 to buffer the downward movement of the push rod 1S.

The method of 'operation is as follows. Initially the contacts lare open, the armature 14 is in its lowermost position, yand the roller 21, and consequently the casing 11, is in its uppermost position, with the roller 21 supported by the maximum radius part of the cam 22 (as illustrated in the drawing).

. 3 The motor 23 is rotated, driving the cam 22, and imparting a cycle of reciprocatory motion to the casing 11, allowing the casing 11 to fall under the iniiuence of gravity or of springs 24 during the initial stroke of the cycle. The casing 11 falls until its lower Iface 11B cornes into contact withthe face 14A of the armature 14 and, if the holding coil 12 is energised, the magnetic flux produced results in a magnetic torce which holds lthe `armature 14 in contact with the lower `face 11B of the casing 11.

Continued rotation of the cam 22 drives the casing 11 to its uppermost position during the return stroke of the cycle; after one complete revolution the motor 23 is stopped. Assuming that the holding coil 12 is energised, the armature 14 moves with the casing 11 so that the push rod 15 is driven upward, springs 26 are compressed, and the contacts 8, 9 are closed.

There are two methods of opening the vacuum switch. In the first, the holding coil 12 is de-cnengised, allowing the magnetic ux to decrease and resulting in a sufiicient reduction in the magnitude of Ithe magnetic lforce so that the force of springs 26 causes the armature 14 to move away trom the lower Itace 11B of the casing 11, and the movable contact 9 travels downward to its open position.

In the second, the holding coil 12 may remain energised, and the trip coil 13 is energised-e.g. by a pulseto divert the magnetic ilux from the armature 14 and thus sufficiently reduce the magnitude of the magnetic force holding the surface 14A of the armature 14 in contact with the casing 11, so that the springs 26 cause the contacts to open, as in the tirst method. As the flux is diverted rather than destroyed, the trip coil 13 may be of low inductance.

Although the vacuum switch has been described in the vertical position, it may be used in any other position using suitable springs 24.

In place of the motor-driven cam 22, any other suitable means may be used to impart a cycle of reciprocatory motion to the casing 11; such means may be electrical, mechanical, hydraulic or pneumatic.

In accordance with vacuum switch practice the fixed contact 8 may be spring loaded towards the movable contact 9 and may be mounted so as to be capable of limited `axial movement, and the movable contact 9 may lbe c-onnected to the push rod 15 through a compressi-ble coupling means, so that the iixed contact 8 may move with the movable contact 9 to compress the spring loading the iixed contact 8 towards the movable contact 9, and the push rod 15 may move relative to the movable contact 9 to compress the compressi-ble coupling means and load the movable Contact 9 towards the fixed contact 8 upon initial closure of the contacts 8, 9. In such an embodiment, when the contacts 8, 9 a-re closed, the spring loading on the iixed contact 8 and the yforce exerted by the compressed compressible coupling means both act upon the push rod 15 in the same sense `as the release springs 26 `and thus tend to separate the face 14A of the armature 14 from the face 11B of the casing 11. It will be appreciated that, when such spring loaded contacts are employed, the release springs 26 may be dispensed with.

It will be understood that in order to enable a load of (say) 500 lbs. to be applied to the contacts 8, 9 when they are in the closed position either the xed contact 8 should be spring mounted or the Imovable contact 9 should be connected to the push rod 15 through 'a compressible coupling means as described above, or alternatively` the motor 23 Idriving the cam 22 should -be resiliently mounted.

The release springs 26 may be replaced by any other suitable means of providing the desired force acting on the actuating means in the direction of the initial stroke of the cycle; such alternative means may conveniently provide lfor variation ofthe force, and thus for variation of the switch opening speed; this alternative means may be other mechanical lmeans, or electrical, hydraulic, or pneumatic means.

Two or more interrupters may be operated by a single 4 actuating mechanism, by provision of a suitable interconnection.

Where lthe -irst method described above of opening the switch is not required-sometimes referred to as novolt release action-the holding coil 12 may be replaced by `a permanent magnet as a means of producing magnetic flux.

I claim:

1. In a magnetic actuator having movable actuating means; a co-operating element; biasing means biasing said movable actuating means to one position; and magnetic flux pnoducing means yfor producing a magnetic force which holds said movable actuating means and said cooperating element together, the improvement comprises:

(i) said co-operating element being movable;

(ii) cam and cam follower means connected to the movable cooperating element to impart to the movable co-operating element a cycle of reciprocatory motion having an initial stroke for moving said movable co-operating element into contact with said movable actuating means to enable them to be held together by operation of said magnetic flux produci ing means, and a return stroke for moving said actuating means and said movable co-operating element together against the bias of said biasing means; and

(iii) means reducing the magnitude of said magnetic torce holding said movable actuating means `an-d said lmovable co-.operating element together so as to permit said biasing means to move said movable actuating means away from said movable co-operating elements.

2. In a magnetic actuator having movable lactuating means; a co-operatirig element; biasing means biasing said movable actuating means to one position; and magnetic flux producing means for producing a magnetic force which holds said movable actuating means and said cooperating element together, said magnetic ilux producing means being being housed within said co-operating element; the impnovement comprises:

(i) said co-operating element being movable;

(ii) cam and cam follower means connected to the lmovable co-operating element so as to impart to said movable co-operating element a cycle of linear reciprocatory motion lhaving .an initial stroke for moving said movable co-operating element into contact with said movable `actuating means to enable them to be held together by operation of said magnetic flux producing means, and a. return stroke for moving said actuating means and said movable co-'operating element together against the bias [of said 'biasing means; and

(iii) trip coil means housed within said movable cooperating element and energizable so as to divert magnetic flux produced by said magnetic flux producing means away from said movable actuating means so that said movable actuating means is moved away from said movable co-operating element by said biasing means.

3. In a magnetic actuator according to claim 1 wherein the improvement further comprises said movable cooperating elernent comprising casing means housing said magnetic flux producing means.

4. In a magnetic actuator according to claim 1 wherein the improvement tur-ther comprises said magnetic ux producing means comprising an electromagnetic device.

5. In a magnetic actuator according to claim 4 wherein the improvement further comprises said means for reducing the magnitude of said magnetic force comprising means to de-energise said electromagnetic device.

6. In a magnetic actuator according to claim 4 wherein the improvement further comprises said means for reducing the magnitude of said magnetic force comprising a trip coil.

7. In a magnetic actuator according to claim 1 wherein the improvement further comprises said magnetic flux producing means comprising a permanent magnet and said means Ifor reducing the magnitude of said magnetic force comprising a trip coil.

8. In a magnetic actuator according to claim 3 wherein the improvement further comprises:

(i) said casing means having an annular part defining a bore, and

(ii) said movable actuating means comprising rod means and an armature plate, said rod means being secured to and protruding from a face of said armature plate and extending through said bore.

9. In a magnetic actuator according to claim 8 wherein the improvement further comprises:

(i) said rod means carrying flange means on the side of said annular part remote from said armature plate, and

(ii) said biasing means comprising spring means acting upon said flange means.

10. An electric switch including a pair of co-operating contacts, one of which is movable, and having associated References Cited UNITED STATES PATENTS 3,248,497 4/ 1966 Lindsay. 3,253,098 5/1966 Perry 335-170 BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner U.S. Cl. X.R. 200-144; 335-170 

